Generally, a dimming driver circuit can be used to adjust the brightness of a lighting device. A conventional dimming driver circuit comprises a power converting unit, a control unit and a current detection resistor. The power converting unit receives an input voltage and converts the input voltage into an output voltage. The output voltage is outputted to a light-emitting element in order to illuminate the light-emitting element. The current detection resistor is serially connected with the power converting unit for detecting the output current from the power converting unit and generating a corresponding detecting voltage signal. The detecting voltage signal is the voltage difference between the two ends of the current detection resistor. The control unit is electrically connected with the power converting unit and the current detection resistor for receiving the detecting voltage signal and a dimming signal and comparing the detecting voltage signal with the dimming signal. According to the comparing result, the magnitude of the output current from the power converting unit is adjusted to comply with the dimming signal.
In the close-loop control system, the control unit of the conventional dimming driver circuit usually employs the analog dimming technology. However, the analog dimming technology faces a challenge. That is, the precision of the output current is usually unsatisfied because a current detection resistor is used to detect the current. The tolerance, deviation and delay of the analog dimming technology result in a relatively fixed error. Under this circumstance, the precision of the output current is reduced, and the output current cannot be designated or controlled. Since the output current from the power converting unit cannot be precisely adjusted according to the dimming signal, the purpose of widening the dimming range cannot be achieved.
Moreover, the conventional dimming circuit uses a single dimming technology to adjust the brightness of the light emitting diode. For example, the dimming range for the analog dimming technology is in the range between 10% and 100%. Moreover, the dimming range for the PWM dimming technology is in the range between 1% and 100%. However, in many situations such as the scene lighting situation or the building lighting situation, plural light emitting diodes generate different color light beams. Under this circumstance, the dimming range for each light emitting diode should be as wide as possible. For example, the dimming range for the light emitting diode has to be in the range between 0.1% and 100%, or even in the range between 0.01% and 100%. In other words, the conventional dimming driver circuit cannot achieve the above purpose.
Therefore, there is a need of providing a dimming driver circuit and a control method in order to overcome the drawbacks of the conventional technologies.